Receiving apparatus for train communication systems



March 24, 1942. D.- WHITELOCK RECEIVING APPARATUS FOR TRAINCOMMUNICATION SYSTEMS Filed Dec. 51, 1940 BPF IN NTOR Lela 12:10.zzeloclz HIS ATTORNEY Patented ar. 2c, 1942.

2,277,469 RECEIVING APPARATUS FOR TRAIN MMUNI Leland D. Whitelock, WiThe Union Switch &

CATION SYSTEMS lkinsburg, Pa., assignor to Signal Company, Swissvaie,Pa., a corporation of Pennsylvania Application December 3.1, 1940,Serial No. 372,475

6 Claims.

other side band being suppressed. In such a sys-' tem a calling orsignaling current equivalent to the carrier modulated by a preselectedfrequency within the voice frequency range is employed for calling andsignaling. The receiving apparatus includes a demodulator operable todemodulate and pass only the voice frequency energy to a telephonereceiver or loud speaker at which device speech is reproduced inresponse to reception of such telephone current. When the calling orsignaling current is received then energy of the single preselectedfrequency appears in the output of the. demodulator and this callingcurrent is used to govern a suitable signaling or calling device, suchas a lamp or electric bell. The loud speaker may be normally held at aninactive condition and switched to an active condition upon reception ofthe calling calling or signaling current may be transmitted continuouslyexcept during periods when telephone communication is desired in orderto provide a continuous check on the operative conditionof the apparatusand under such circumstances an indication lamp is normally energized toindicate the operative condition of the apparatus. In this latter casethe loud-speaker is held at an inactive condition as long as thesignaling current is received and is switched to an active conditionwhen such signaling current ceases.

Accordingly a feature of my invention is the provision of receivingapparatus for railway train communication systems incorporating noveland improved means responsive to a signaling current for controllingsignaling devices according to the presence or absence of suchvsignaling current.

Another feature of my invention is the provision of receiving apparatusfor railway train communication systems incorporating novel means forcontrolling a first indicator to display to the operator in attendanceat such receiving apparatus a. steady indication as long as signalingcurrent is received and to display a different indicator upon thetermination of such signaling current as an indication to the operatorthat telephone communication is desired.

Again a feature of my invention is the provision of novel means forreceiving apparatus for train communication systems wherewith the loudspeaker is automatically coupled to the demodu- 1 lator when the callingor signaling current ceases.

current. Again the Another feature of my invention is the provision inreceivingapparatus for train communication systems of efiective andinexpensive calling and signaling means.

The above cited features of my invention 'as well as other advantageswhich will be apparent from the following specification, are attainedaccording to my invention by providing an ionization type of electrontube, a source of alternating current and slow acting relays which arethemselves controlled by the electron tube and which relays in turncontrol a signal lamp and a signal bell and automatically switch a loudspeaker from an inactive to an active condition according as signalingcurrent is or is not received. A filter tuned to pass energy of afrequency corresponding to that of the calling or signaling current isconnected across the'output terminals of the demodulator included insuch receiving apparatus. The source of alternating current anda controlrelay are included in an anode circuit of the electron tube to energizethe relay when the tube -is ionized. The output terminals of the filterare included in the control circuit of the tube and the tubeis. causedto ionize by the energy passed by the, filter when signaling current'isreceived. The anode circuit relay controls theslow acting-relays in sucha manner as to cause the lamp to be illuminated as long as the anodecircuit relay is energized and. picked up. When the signaling currentceases the electron tube deionizes due to the alternating voltage of thesource included in the anode circuit and the anode circuit relay isdeenergized and released to effect a control of the slow acting relays,such control being effective to cause the lamptto be extinguished and anelectric bell to sound during the slow acting period of at least oneslow acting relay. The slow acting relays when thus controlled are alsoeffective to couplethe loud speaker to the output termi-. nals of thedemodulator. Hence the signaling current when continuously receivedcauses the display of the indication lamp as an indication that thesystem is operative and when such signaling c n'rent ceases the bell issounded to indicate to the attendant-at the receiving apparatus thattelephone communication can be expected and the loud speaker iseffectively coupled to the output of the demodulator.

I shall describe one'form of apparatus embodying my invention andshall-then point out the novel features thereof in claims.

The accompanying drawing is a diagrammatic view showing a. preferredform of apparatus embodying my invention. Y

Referring to the drawing the reference character IC designates aninductor mounted on a vehicle of a railway train-in inductive relationto a transmitter circuit, not shown. The inductor IC is preferablymounted in inductive relation to the track rails, the track rails beingincluded in a transmitting circuit to which communication current issupplied at some station remote from the vehicle on which the inductorIC is mounted. This transmitting circuit for transmitting communicationcurrent between two spaced stations along the railway may be thatcovered by Letters Patent of the United States No. 2,112,364, grantedMarch 29, 1938, to L. 0. Grondahl for Electric train signaling systems.

The electromotive forces induced in inductor 6,000 cycles per secondmodulated by voice frequencies for telephone communication and to usethe equivalent of such carrier current modulated by a single preselectedfrequency within the voice frequency range for calling and signaling.Under such circumstances the filter BPF would pass a band extending from6,500 to 8,500 cycles per second, the voicefrequency range being takenas extending from 500 cycles to 2,500 cycles. For signaling the currenttransmitted may be of 7,000 cycles per second which is the equivalent ofthe upper side band of the carrier of 6,000 cycles modulated by thevoice frequency of 1,000 cycles.

The amplifier demodulator AD may be any one of several well-known typesfor such devices and is shown conventionally for the sake of simplicity.It is sufllcient for the present application to point out that theamplifier-demodulator AD includes a normally active source of carriercurrent for mixing with the incoming communication current, and isoperative to cause only the voice frequencies to appear in the output ofthe demodulator, the local carrier and the other products ofdemodulation being suppressed. One or more stages of amplification maybe employed either ahead of demodulation of after demodulation oramplification may be usedboth ahead of and after demodulation. On theassumption the communication current is of the frequency range referredto above then energy of the voice frequency band extending from 500 to2,500 cycles appears at the output terminals of theamplifierdemodulator-AD when telephone current is picked up by inductorIC, and energy of the single preselected frequency of 1,000 cyclesappears at the output terminals of the amplifier-demodulator whensignaling current is picked up by inductor IC. It will'be understood ofcourse that my invention is not limited to the frequencies set forthhereinbefore but such frequencies are used for illustration only.

A filter FI including a reactor 2, a transformer TI and condensers 3 and4 is connected across the output terminals of the amplifier-demodulatorAD, the arrangement being that primary winding 5 of transformer TIcondenser 3 and reactor 2 are connected in series across the outputterminals of the amplifier-demodulator, and condenser 4 is connectedacross secondary winding 6 of transformer TI. The parts of filter Fl areproportioned to pass only energy of the frequency of the signalingcurrent, that is, to pass only energy of 1,000 cycles per second whenthe signaling current is of a frequency assumed hereinbefore.

The apparatus includes an electron tube ET, a source of alternatingcurrent CS and a control relay RI. The tube ET is preferably of the coldcathode gas filled type and is provided with an anode 1, a controlelement 8 and a cathode 9. The current source may be any suitable sourceof alternating current and is shown as comprising a vibrator VB and atransformer T2. operating winding I0 of vibrator VB is connected overits own contact I! to a suitable source of direct current such as theusual train carried 32 volt generator or battery, not shown, but whoseportioning and adjustment of the parts of the vibrator. Armature II whenvibratedalternately engages contacts l2 and I3 and causes current fromthe direct current source to be supplied to two portions of primarywinding I 4 of transformer T2v with the result that an alternatingelectromotive force is induced in secondary winding I5 of transformerT2. The parts are so proportioned that the electromotive force inducedin secondary winding I5 is of, say, volts and of a frequency of, say, 60cycles per second although such voltage and frequency are not essentialand some other voltage and frequency may be selected if desired. Acondenser I 6 is connected across,

.the operation.

Electron tube ET is provided with an anode circuit which includes lowerterminal of secondary winding I5 of transformer T2, anode 1 andintervening tube space to cathode 9 of tube ET, winding I9 of relay RIand a condenser 20 in parallel and thence to the upper terminal ofsecondary winding I5. Relay RI is a direct'current relay of the usualacting type. A control circuit for tube ET includes secondary winding Iiof transformer Tl connected across control element 9 and cathode 9 oftube E'If, a resistor 2| being preferably interposed in the connection.When no electromotive force is applied to' control element 9 of tube ETthe voltage applied across anode I and cathode 9 from secondary windingI! of transformer T2 fails to ionize the tube and no current flows andrelay RI is deenergized and released. When a sufiicient voltage isapplied to control element 9 to drive control element 8 positive inpotential with respect to cathode 9. ionization is effected for tube ETand current flows in the anode circuit. The parts are so proportionedthat when signaling current is received and energy passed by filter FIthe positive half cycle of such energy drives control element 8 positivein potential with respect to cathode 9 and tube ET is ionized, and sincethe signaling current energy passed from 'filter F'l is- RI serving tosmooth out the rectified current.

When there is either no voltage or a relatively aaraaee low voltageapplied to control element 8, the tube ET deionizes during the negativehalf cycles of the alternating current supplied to the anode cir-.

trol element 8 of tube ET may effect ionization with the result thatrelay RI may be momentarily picked up but such momentary operation ofrelay RI will not be effective to change the control eifected by relayRI over a slow acting relay as will be shortly described.

The apparatus also includes two slow release relays R2 and R3, a signallamp LI, a signal bell BI and a loud speaker LS. Relay R2 is energizedover an obvious circuit including back contact 22 of relay RI and relayR3 and lamp LI are controlled in parallel over an obvious circuitincluding front contact 29 of relay RI and back contact 23 of.relay R2.Bell BI is controlled over a circuit including terminal B32, frontcontact 24 of 'relay R2, front contact 25 of relay R3, winding of hellBI and terminal N32. .The circuit for the loud speaker LS can be tracedfrom the upper right hand output terminal of amplifier-demodulator ADover the operatingwinding of loud speaker LS, front contact 26 of relayR2, ground electrodes 21 and 28 and to the lower right-hand outputterminal of the amplifier-demodulator.

It is clear that when signaling current is re ceived and relay RI ispicked up, due to the ionization of tube ET, relay R2 is released andrelay R3 is picked up and lamp LI is illuminated, the illumination oflamp LI being an indication to the attendant at the receiving apparatusthat signaling current is being received and that the ing up opens backcontact 23 and closes front contacts 26 and 24. The lamp LI isextinguished as soon as relay RI is released to open front contact 29and its circuit is then held open at back contact 23 of relay R2 whenrelay R2 is picked up. Relay R3 is also deenergized when relay RI isreleased but relay R3 does not release until the end of its slow releaseperiod, and during the slow release period of relay R3 the I bell Bl issupplied ,with current to provide an pears in the telephone current sothat energy is passed by filter Fl to the control circuit of tube ET,the tube ET may be caused to ionize with the result that relay RI ispicked up. Such voice frequency will persist in the telephone currentonly for a relatively short interval and hence relay RI will be pickedup for only a short in-. I

terval so that relay R2 which is controlled over back contact 22 ofrelay RI will not release due to its slow release characteristic duringthe short interval that relay RI may be picked up when telephone currentis received. When the telephone current cease and signaling current isagain transmitted causing relay RI to be picked up for an extendedperiod of time, then relay R2 I is deenergized and released at the endof its slow release period causing lamp LI to be illuminated,

relay R3 to be picked up and the loud speaker LS I to be disconnectedfrom the amplifier-demodulator with the net result that the apparatus isrestored to its normal condition, that is to the condition shown in thedrawing.

It is to be noted that-relay R3 and lamp LI are controlled over acircuit that includes a front contact 29 of relay RI and a back contact23 of relay-R2 and a failure of relay R2 will not cause a false displayof lamp LI and false energization of relay R3. It is also to be notedthat a normal bias voltage may be readily provided for control element 8of tube TI by including a battery or other source of voltage in thecontrol circuit of the tube. Also if .it seems desirable to providemeans for changing the sensitivity of the discharge tube ET suchadjustment can be made by placing a voltage divider across the output ofthe source of alternating current and connecting the movable contactmember of such voltage divider to the anode I of the tube. Such voltagedivider would also provide a bias voltage for the control element 8 ofthe tube.

It is to be seen therefore that I have provided simple and inexpensivereceiving apparatus for Y railway train communication systems wherewitha first signal indication is continuously displayed in response toreception of a signaling current to indicate an active condition of theapparatus and a second and diflerent signal indication is displayed fora short period of time when such signaling current ceases to indicate tothe attendant at the receiving apparatus that he may expect telephonecommunication. Also the loud speaker is automatically switched from aninactive to an active condition when signaling current ceases and isthen restored to its inactive condition when signaling current is againtrans- 4.x

mitted.

Although I have herein shown and described but one form of receivingapparatus for train communication systems embodying my invention,

it is understood that various changes and modifications may be madetherein within the scope of the appended claims without departing fromthe spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. Receiving apparatus for a train communication system comprising,a'demodulator capable of demodulating a signaling current which is theequivalent of a carrier current modulated by a preselected frequency, afilter having its input terminals connected to the output terminals ofsaid demodulator and tuned to pass energy of I said preselectedfrequency only, an ionization type of electron tube. a source ofalternating current. a relay, an'anode circuit including saidalternating current source and said relay connected across the anode andcathode of said tube to energize the relay when the tube is ionized, acontrol circuit including the output terminals of said filter connectedacrossthe control element and cathode of said tube to cause ionizationof the tube by the energy passed by said filter, a signal lampcontrolled by a front contact of said relay to indicate reception ofsaid signaling current, an electric bell, and circuit means includingacontact of said relay and a slow acting device to cause energization ofsaid bell for a predetermined period when the relay is released upontermination of the signaling current.

2. .Receiving apparatus for a train communication system comprising, ademodulator capable of demodulating a signaling current which is theequivalent of a carrier current modulated by a preselected frequency, afilter having its input terminals connected to the output terminals ofsaid demodulator and tuned to pass energy of said preselected frequencyonly, an ionization type of electron tube, a source of alternatingcurrent, a control relay, an anode circuit including said alternatingcurrent source and said control relay connected across the anode andcathode of said tube 'to energize the relay when the tube is ionized, acontrol circuit includingthe output terminals of said filter connectedacross the control element and cathode of said tube to cause ionizationof the tube by the energy passed by said filter, a first and a secondslow release relay, a signal lamp, an electric bell, means including aback contact of said control relay to energize said first slow releaserelay, means including a back contact of said first slow release relayto energize said second slow release relay and said signal lamp inparallel, and means including in series a front contact of said firstslow release relay and a front contact of said second slow release relayto energize said electric bell.

3. Receiving apparatus for a traincommunication system comprising, ademodulator capable of demodulating a signaling current which is theequivalent of a carrier current modulated by a preselected frequency, afilter having its input terminals connected to the output terminals ofsaid demodulator and tuned to pass energy of said preselected frequencyonly, an ionization type of electron tube, a source of alternatingcurrent, a control relay, an anode circuit including said alternatingcurrent source and said control relay connected across the anode andcathode of said tube to energize the relay when the tube is ionized, acontrol circuit including the output terminals of said filter connectedacross the control element and cathodeof said tube to cause ionizationof the tube by the energy passed by said filter, a first and a secondslow release relay, a signal lamp, an electric bell, a circuit includinga back contact of said control relay to energize said first slow releaserelay, a circuit in: cluding in series a front contact of said controlrelay and a back contact of said first slow release relay to energizesaid signal lamp and said second slow release relay in parallel, and acircuit including in series a front contact of said first slow releaserelay and a front contact of said second slow release relay to energizesaid bell.

4. Receiving apparatus for a train communi-- cation system comprising,a'demodulator capable of demodulating a carrier telephone current and asignaling current equivalent to such carrier modulated by a preselectedfrequency, a filter having its input terminals connected to the outputterminals of said demodulator and tuned to pass energy of saidpreselected frequency only, an ionization type of electron tube, asource of alternating current, a relay, an anode circuit including saidalternating current source and said relay connected across the anode andcathode of said tube to energize the relay when the tube is ionized, acontrol circuit including the output terminals. of said filter connectedacross the control element and cathode of the tube to cause ionizationof the tube by the energy passedby said filter, a signal controlled overa front contact of said relay to indicate reception of said signalingcurrent, a loud speaker, and means controlled over a back contact ofsaid relay to effectively couple said loud speaker to the outputterminals of said demodulator for reproduction of speech upon receptionof said telephone current.

5. Receiving apparatus for a train communication system comprising, ademodulator capable of demodulating a carrier telephone current and asignaling current equivalent to such carrier modulated by a preselectedfrequency, a filter having its input terminals connected to the outputterminals of said demodulator and tuned to pass energy of saidpreselected frequency only, an ionization type of electron tube, asource of alternating current, a relay, an anode circuit including saidalternating current source and said relay connected across the anode andcathode of said tube to energize the relay when the tube is ionized, acontrol circuit including the output terminals of said filterconnected'across the control element and cathode of the tube to causeionization of the tube by the energy passed by said filter, a signallamp controlled over a front contact of said relay to indicate receptionof said signaling current, a loud speaker, means controlled over abackcontact of said relay to v effectively couple said loud speaker to theoutput terminals of said demodulator for reproduction of speech uponreception of said telephone current, an electric bell, and a slow actingmeans controlled. over contacts of said relay to energize said bell'forthe slow acting period of said slow acting means when therelay isreleased upon termination of the signaling current.

6. Receiving apparatus for a train communication system comprising, ademodulator capable of demodulating a carrier telephone current and asignaling current equivalent to such carrier modulated by a preselectedfrequency, a filter having its input terminals connected to the outputterminals of said demodulator and tuned to pass energy of saidpreselected frequency only, an ionization type of electron tube, asource of alternating current, a control relay,-an anode circuitincluding said alternating current source and said control relayconnected across the anode and cathode of said tube to energize therelay when the tube is ionized, a control circuit including the outputterminals of said filter con.- nectedacross the control element andcathode of the. tube to cause ionization ofthe tube by the energy passedby said filter, a first slow release relay energized over a back contactof said control relay, a' second slow release relay energized over aback contact of said first slow release relay, a'signal lamp energizedover a back contact of said first slow release relay to indicatereception of'said signal current, an electric bell energized over afront contact of each of said first and second slow release relays inseries to sound a warning for the slow release period of said secondslow release relay when said signal ing current ceases, and a loudspeaker effectively connected to the output terminal of said'demodulatorover a front contact of said first slow release relay to reproduce thespeech when telephone current is received. A LELAND D. WHITELOCK.

